The present invention relates to a system for controlling or adjusting an electromechanical brake.
An electromotive brake with these features is described in U.S. Pat. No. 4,995,483. The system disclosed is used to decelerate aircraft, however, its principal structure is applicable on road vehicles as well. The brake includes a set of brake discs and an associated set of friction discs which are urged against each other by way of a clamping device. The clamping device is actuated electromotively by way of a spindle, which is driven by a roller thread drive and pressed against the outward friction disc. A force-measuring element is interposed between the first friction disc and the spindle head. A clearance is provided between the brake discs and the friction discs.
The general point is that to produce a brake force, first the clearance must be overcome. Only after the friction discs or friction elements abut on the brake discs is it possible to transmit a clamping force which causes deceleration of the wheel connected to the brake discs. To apply the friction discs on the brake discs, i.e., to overcome the clearance, only low forces are transmitted which should not exceed a defined limit value.
As soon as a limit value is exceeded, the system disclosed in the above U.S. patent interprets this fact as application of the friction discs on the brake discs.
The associated angular position of the driving electric motor is defined as the zero position.
To produce a clamping force, the motor can be readjusted by defined amounts of angle, and the interrelation between the readjustment of the motor based on the zero position and the clamping force exerted is taken into account.
When the brake is released, the spindle is initially restored until the zero position is reached. Subsequently, the spindle is reset by a further amount which corresponds to the clearance. This type of clearance adjustment is very inaccurate, and, in addition, it may only be effected during brake application. It is not possible to adjust the clearance independently of a braking operation.
The provision of a force sensor is absolutely necessary in the brake disclosed in the above-mentioned U.S. patent in order to be able to determine the neutral or zero position. The problem is that the signal of such force sensors is subjected to a drift so that it is only possible to determine the actual force exerted by using major electronic means. Therefore, the objective of development is to obviate the need for a sensor of this type and to derive the necessary data for brake application from the signals of other sensors, for example, a sensor which senses the wheel rotational speed.
However, this eliminates the possibility of performing the method of determination of the neutral position mentioned in the above U.S. patent.
Therefore, an object of the present invention is to provide a controlling or adjusting system which permits adjustment of a clearance even without the use of a force sensor.
Another object of the present invention is to provide a controlling or adjusting system to identify and readjust the clearance which operates independently of brake application and, in addition, permits readjusting the clearance even during travel of the automotive vehicle.